Cell biology international reports最新文献

Three colon cancer cell lines (Colo 205, HT29 and T84) were investigated by X-ray microanalysis with respect to elemental composition and the effect of cAMP on the cellular concentrations of Na, K, and Cl. The cultures were not homogeneous with respect to their elemental composition, but appeared to consist of two sub-groups, low-K cells and high-K cells. In all three cell lines, the low-K cells had, in addition, higher Ca, markedly lower Cl, and somewhat lower P and S concentrations. Differences in Na and Mg concentrations were absent or not consistent. Exposure of cells to cAMP caused a decrease of the cellular Cl and K content in high-K (high-Cl) cells. Changes in Na were not significant. No difference between the three cell lines could be noted. Incubation of the cells with phorbol myristate acetate (PMA), which has been shown to down-regulate the expression of the cystic fibrosis (CF) transmembrane conductance regulator gene and thus confer CF-like characteristics on the cells, significantly decreased the response in the cellular Cl concentration to cAMP stimulation. It is concluded that cAMP initially activates predominantly the apical Cl⁻ channel and the basolateral K⁺ channel.

A high-speed supernatant extract was obtained from infective oocysts of Eimeria tenella homogenised in a sucrose-low ionic strength buffer. Immunoblotting showed this soluble, micropore-filtered preparation (designated E1) to be rich in actin. E1 underwent superprecipitation on addition of ATP but not its non-hydrolysable analogue AMP.PNP — behaviour typical of an actomyosin solution. The superprecipitate fluoresced strongly in the presence of rhodamine-phalloidin (indicative of the presence of F-actin) and electron microscopy of negatively-stained preparations of this flocculent matter confirmed the abundance of filamentous material within it. This is the first demonstration of a functional actomyosin isolated from a member of the economically important phylum Apicomplexa.

The morphology and the polypeptide composition of the nuclear matrix obtained from 37°C incubated nuclei has been studied in mouse erythroleukemia cells. From a structural point of view, in the absence of heat treatment, the matrix lacked identifiable nucleolar remnants and the internal fibrogranular meshwork whereas a peripheral lamina was seen. On the contrary, the matrix obtained from heat exposed nuclei displayed very electrondense nucleolar remnants and an abundant inner network. These results were obtained irrespective of the type of extracting agent (2M NaCl or 0.2 M (NH₄)₂SO₄) used to remove histones and other soluble proteins. The heat stabilization of the matrix could not be prevented by sulfhydryl blocking chemicals such as iodoacetamide and n-ethylmaleimide, thus suggesting that heat does not stabilize the matrix by inducing the formation of disulfide bonds. Only limited differences in the polypeptide pattern of matrix isolated under different conditions were seen using one-dimensional pore gradient polyacrylamide gels stained with both Coomassie Brilliant Blue and silver despite the fact that the matrix fraction from heat treated nuclei retained about three fold more protein in comparison with controls. The same results were obtained also by means of two-dimensional non- equilibrium gel electrophoresis.

The effects of Bombina variegata cutaneous venom (Bvv) on eukaryotic cell growth has been assessed employing the human leukaemic cell line HL 60, by liquid and agar semisolid cultures and ⁵¹Cr release assay. HL 60 cells growth is impaired by Bvv in a dosedependent fashion in both culture systems. The arrest of proliferation requires a contact time lower than 3 min and it is not reversed by washing and culturing the cells in a Bvv-free medium. Similarly, an extremely short exposure time is needed to determine maximum ⁵¹Cr release. Neither the agar medium nor the fetal calf serum interact with Bvv effects, which, according to the above findings, must be regarded as cytolytic in nature. In both liquid and the agar-semisolid culture Bvv cytolytic activity half life is about 8 hr.

The cytolytic properties of Bvv are thought to be part of the chemical defence system of amphibian skin.

Insulin-like growth factors (IGFs) I and II (IGF-I, IGF-II) and Des-3-IGF-I at physiological concentrations are potent mitogens of bovine undifferentiated mammary epithelial cells cultured in collagen in a serum-free medium. Des-3-IGF-I was found to be as potent as IGF-I, while IGF-II was significantly less active. All three factors acted either synergistically or additively with epidermal growth factor (EGF), cholera toxin and fetal calf serum (FCS). Indirect evidence indicates that despite its lower mitogenic activity the action of IGF-II is mediated through IGF-I receptors. The galactopoietic activity of Des-3-IGF-I and IGF-II was studied in an organ culture of bovine lactating mammary glands using lactogen-responsive fat synthesis as a test. Neither Des-3-IGF-I nor IGF-II exhibited galactopoietic activity nor did they affect the galactopoietic activity of prolactin.

Cell proliferation and cell death appear in several systems as mutually exclusive, which raises the assumption that a same factor or secondary signal(s) might exert opposite control on the two processes. To test this assumption we investigated the time-course evolution of the S phase and apoptotic indices in rat liver during cyproterone acetate (CPA) induced hyperplasia and during the recovery of normal liver mass provoked, respectively, by cyproterone acetate (CPA) treatment and withdrawal.

The levels of c-myc and c-ras transcripts were also followed in view of the indications of a positive role of these oncogenes in proliferation.

The data showed that proliferation and cell death are not always mutually exclusive and that a high rate of cell death was indifferently associated with high or low c-ras expression. Our data are consistent with a role of this gene in proliferation but exclude that it plays an opposite role in controlling cell death.